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C ompression Molding

C ompression Molding . Jonathan Chodosh , Sherif Madkour , Jesse McGrath. Compression Molding: What?. Is a processing technique that combines forming the product along with simultaneous curing of the resin. High Pressure Higher Temperature Curing Agent. Development.

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C ompression Molding

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  1. Compression Molding Jonathan Chodosh, SherifMadkour, Jesse McGrath

  2. Compression Molding: What? • Is a processing technique that combines forming the product along with simultaneous curing of the resin. • High Pressure • Higher Temperature • Curing Agent

  3. Development • 1909 whenLeo Hendrik Baekeland • phenol-formaldehyde resins • Patents on a automatic compression machine date back to 1930 • Development of C.M was hindered by reaction knowledge.

  4. Thermosets • Heat compression causes an irreversible chemical charge in the plastic which solidifies the part . • The plastic won’t soften, so the mold doesn’t need to be cooled. • After short interval, the press is opened and the molded part is removed. • Any plastic remaining in the mold is removed by compressed air. The operator breaks the flash.

  5. Thermoplastic • Preheated in a dielectric heater. • The mold is cooled to a point where the plastic retains enough integrity to be removed from the mold without partial distortion. • The same steps used for thermosets are repeated here as well.

  6. Advantages • Molds are inexpensive • Labor costs vary • Great for large parts • Minimum waste • Dimensional accuracy • Warping and shrinkage minimized • Fast cycle(1-5 minutes) • High volume output • High quality surfaces • Complex parts

  7. Disadvantages • No delicate pieces • Uneven parting lines • High initial investment • secondary operations (e.g. trimming) • Mold depth is limited • Product consistency

  8. Considerations • Mold heating • Temperature, heating rate and heating method • Compression rate • Max compression force • Curing time • How long until part can be removed from mold. • Mold cooling rate • Mold cycling rate

  9. Equations T*= (T-T0)/(T0-Tad) = Reduced Temperature t*= (xt)/(h’)2 =Reduced Time y*= y/h = distance form slab centerline T0=Original Temperature Tad=Adiabatic Temperature X=Thermal Diffusivity h’=Heat Transfer Coefficient between. Mold and polymer h= half thickness of slab.

  10. Thermoset Thermoplastic • Bulk molding compound (BMC) • Sheet molding compound (SMC) • Unidirectional tapes • Woven Fabrics • Chopped Strands • Randomly oriented fabrics • Preforms • Pellets • Sheets • Extruded Elastomers • Extruded Range of Materials

  11. Typical Products • Automotive parts • Hoods, bumpers, fenders, spoilers, etc. • Medical equipment • Caps and plugs to blood separation machines and ultrasound equipment • Aerospace • Electrical connectors to guided missiles

  12. http://www.rdmoulds.com/rdmoulds/ma/24%20front%20bumper%20molds.jpghttp://www.rdmoulds.com/rdmoulds/ma/24%20front%20bumper%20molds.jpg http://www.tqc.co.uk/images/bumper7.jpg

  13. http://www.compositesworld.com/uploadedimages/Publications/CW/Articles/Internal/hoodHyundai.jpghttp://www.compositesworld.com/uploadedimages/Publications/CW/Articles/Internal/hoodHyundai.jpg

  14. Transfer Molding • Hybrid between Injection and Compression molding • Cross linking reaction is started prior to placement in the mold • Resin is heated and put under pressure • “Slushy mix” is then forced into the Mold. • This point on Transfer molding follows the Compression molding process.

  15. Advantages Disadvantages • Rapid production rates • Largest Benefit over C.M. • Geometrical Accuracy • Intricate Parts Possible • Expensive molds • Expensive equipment • Much material loss • Size limitations of products Benefits/Constraints of T.M.

  16. References • http://composite.about.com/library/glossary/c/bldef-c1203.htm • http://twistertechnology.com/Process%20Capabilities.html • http://www.me.gatech.edu/jonathan.colton/me4793/compmold.pdf • http://www.daprorubber.com/index.aspx • http://www.rdmoulds.com/rdmoulds/ma/24%20front%20bumper%20molds.jpg • http://www.tqc.co.uk/images/bumper7.jpg • http://www.compositesworld.com/uploadedimages/Publications/CW/Articles/Internal/hoodHyundai.jpg • http://www.bsu.edu/web/jebutcher/compressionmolding.htm

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